1. Field of the Invention
The invention relates to an arrangement with at least one superconductive cable and a cryostat which surrounds the cable, wherein the cryostat has at least one thermally insulated pipe which encloses the superconductive cable and a hollow space for conducting a cooling agent there through, wherein the cryostat, in the same manner as the superconductive cable located in the cryostat, is constructed for connection to stationary parts of a transmission path for electrical energy.
2. Description of Related Art
Such an arrangement is disclosed, for example, in EP 1 617 537 Stationary parts of the transmission path may be end closures or connecting sleeves by means of which two lengths composed of cryostat and cable are connected to each other.
A superconductive cable includes electrical conductors of a material which changes over into the superconductive state at sufficiently low temperatures. The electrical direct current resistance of a correspondingly constructed conductor is zero with sufficient cooling, as long as a certain current, the critical current, is not exceeded. Suitable superconductive materials are for example, oxidic materials on the basis of rare earths, (ReBCO), in particular YBCO (yttrium-barium-copper oxide), or BSCCO (bismuth-strontium-calcium-copper oxide). Sufficiently low temperatures for placing such a material into the superconductive state are for example, between 67K and 110K. However, there are also superconductive materials, such as for example magnesium diboride, which have to be cooled down even further if they are to change into the superconductive state. Suitable cooling agents for all these materials are for example, nitrogen, helium, neon, and hydrogen or mixtures of these materials.
Accordingly, during operation of an arrangement with at least one superconductive cable, the cable is significantly cooled within the cryostat which causes it to become shorter due to thermal contraction. In order to ensure operability of the transmission path, precautions must be made through which the reduction in length of the cable can be compensated.
The Journal of Physics, Vol. 234, No. 3, 22 Jul. 2010, Pages 1 to 6, describes a to path with respect to cooling of a superconductive cable. The cable is mounted in a cryostat which, in a curved configuration with a length of 16 m, is arranged between two end points which are designated as cryostats A and B. At each of these end points a single bellows is mounted in the cryostat which extends in this area in an unchanged straight line.
US 2010/0285968 A1 discloses a method for compensating a thermally caused reduction in length of a superconductive cable as the cable cools. The construction of a corresponding arrangement provides for a central tension proof structural component. The document also discloses that an undulated jacket composed of thin metal is provided.
EP 0 807938 A1 discloses a sleeve for electrical superconductive conductors which has four radially separated pipes. The pipes have alternating straight sections with high mechanical stability and transversely undulated sections so that the sleeve, which is stiff per se, becomes bendable.
In accordance with US 2006/0211579 A1, straight sections of a superconductive cable constructed as a pipe are connected to each other by means of bellows. The purpose of this is to absorb the effects of earthquakes and for compensating for the unevenness of the ground.
In the arrangement according to EP 1 720 176 B1, a superconductive cable is mounted in a cryostat in such a way that it has the shape of a shaft or helix at room temperature. The resulting excess length of the cable as compared to the cryostat is stabilized by a cross-like network which is connected to the cable in a point by point manner.
EP 1 617 537 B1 mentioned in the beginning discloses an arrangement with a superconductive cable placed in a cryostat, wherein the cable is connected to an end closure. The electrical conductor of the end closure is equipped with a pipe shaped structural component which has radially resilient lamellae of an electrically conductive material into which the conductor of the superconductive cable protrudes in the assembled state. In the case of thermally caused length changes, the superconductive cable can slide in its longitudinal direction in the pipe shaped structural component.